Ultrahigh molecular weight, high tenacity filaments based on spun polyolefins are described in numerous patents, published patent applications, and technical articles. Exemplary references include Kavesh et al. U.S. Pat. No. 4,413,110; Smith et al. U.S. Pat. No. 4,344,908; Smith et al. U.S. Pat. No. 4,422,993; Kavesh et al. U.S. Pat. No. 4,356,138; Maurer EP 55,001; Harpell et al. U.S. Pat. No. 4,455,273; Kavesh et al. U.S. Pat. No. 4,897,902; Neal U.S. Pat. No. 5,277,858; and Kirkland et al. WO 94/00627.
These filaments are generally made from linear polyethylene or polypropylene chains of a molecular weight of at least 400,000, a tenacity of at least 15 grams per denier (g/d), a tensile modulus of at least 500 g/d (nylon monofilaments are about 20-50 g/d), a melting point of at least 140.degree. C., have high abrasion resistance, low stretch, high toughness, good dimensional and hydrolytic stability, and high resistance to creep under sustained loads. The yarns are opaque and white in appearance. Such yarns are commercially available from Allied-Signal, Inc., Morris, N.J. as SPECTRA fiber and from DSM, NV, Netherlands under the name DYNEEMA. The filaments in these commercial yarns has a significantly higher molecular weight than 400,000.
Both SPECTRA and DYNEEMA filaments are fundamentally made in the same way. A solution containing polyethylene gel swelled with a suitable solvent is spun into filaments of high molecular weight polyethylene. The solvent is removed, and the resulting yarn is stretched or "drawn" on one or more stages. In general, such filaments are known in the art as "gel spun polyolefins" with gel spun polyethylene being the most commercially sold.
Monofilament fishing lines of high molecular weight, gel spun polyolefin filaments in sufficient diameter are not commercially available. The most likely reason is that the filament manufacturing process involves quantities of solvent that must be removed from the filament following its formation. Thicker filaments would hinder the efficiency and completeness of the solvent removal process and aversely affect the strength of the finished filament. In addition, there are concerns for the degree of limpness such lines might have as well as the handling characteristics of such lines in real fishing conditions.
Fishing lines must be reasonably limp to be effective under the conditions of normal fresh and salt water fishing. For example, the bending modulus of nylon monofilaments is within the range from about 15-50 g/d. The high molecular weights characteristic of gel spun polyolefins, however, make the line unacceptably stiff at the diameters generally required for fishing lines, if such lines could be produced. Monofilaments from such materials would not wind onto a conventional reel easily and would be difficult to tie into knots, such as those used to secure a lure to the line, without weakening the line and jeopardizing the quality of the knot.
It would be desirable to have a fishing line from gel spun polyolefins that was sufficiently limp like monofilaments to use for fresh and salt water fishing with conventional fishing equipment and lures.
Fishing lines made from braids of gel spun polyethylene yarns have been introduced into competition with conventional braided fishing line materials (generally polyesters) and nylon monofilament lines. The higher strength of such braided polyethylene lines is a distinct advantage. Such braids can, however, exhibit some disadvantageous characteristics.
Monofilament lines are generally more preferred for bait casting, spinning, and spin casting. Monofilaments have a round, firm structure that makes for more convenient handling. The stiffer nature of the line and the smoother surface combine to reduce drag during the cast and enable longer casts while providing a better release from a fishing reel. Monofilament lines do not entrap water and do not present an outer surface that is vulnerable to snags and entanglement.
Braided lines can also have the tendency to fray at the end of the line. When tied into a knot, this "tag end" frays to create a fuzzy protrusion that can adversely affect the appearance and acceptability of a lure when fishing. In addition, braided lines made from gel spun polyethylenes cannot be cut cleanly with a compression type of line clipper that is commonly in use among anglers. The braid must be cut with a scissors or other type of shearing device to ensure that all filaments in the braid are severed evenly.
It would be desirable to have a line with the high tenacity of gel spun polyolefin lines that is more monofilament-like in its handling characteristics, i.e., the line has a firm structure like that of a monofilament, exhibits a lower diameter than a braid, does not saturate with water, and reduces or eliminates the problems associated with end fraying and the difficulties of cutting the line.
Braided or twisted lines made of gel spun polyolefin yarns are also characterized by an opaque white color (i.e., no light transmittivity). White is not, however, the preferred color for use in a fishing line. There is a belief that white lines are too visible below water and will tend to scare fish from a bait or lure.
It would be useful to have a process for providing a gel spun polyolefin line that exhibited a nonopaque appearance, preferably a translucent to more adequately hide the line when under water.